The nutritional and production costs associated with the development of a competent immune response against nematode parasites is described, based on data from sheep. Anorexia and changes in metabolism are considered to be driven by the host immune response itself and the question is raised about the wisdom of seeking to strengthen immune responses by genetic selection. Several phases of the immune response are identified with different implications for loss of productivity and opportunity for moderation of immune responses and production losses by nutrition. Many animals are able to manage nematode infections with little loss of productivity. In an era when attempts are being made to reduce anthelmintic use and create refugia to reduce the rate of development of drench resistance, treatments based on individual animal performance relative to production targets set by assessment of the prevailing nutritional environment will become more common. These developments, have already occurred in relation to the haematophagic nematodes, for example the "Famacha" technique. Computer-aided weighing and drafting has potential for use with the less pathogenic nematodes prevalent in temperate regions though we need to know more about the pathophysiology and nutritional costs of infections with Nematodirus spp.
host immuno-pathology; nematodes; targeted specific treatments (TST)